1. Field
Example embodiments relate to touch sensing and remote sensing optical touch screen apparatuses.
2. Description of the Related Art
A touch screen apparatus directly receives input data from a display screen. The touch screen executes software functions based on locations of the display screen that are touched by the finger or stylus of a user. Generally, a touch screen apparatus is formed by adding a touch panel to a common display panel. Examples of touch panels include resistance film touch panel, electrostatic capacitance touch panel, surface acoustic wave (SAW) touch panel, infrared ray touch panel, piezoelectric touch panel, etc. Recently, such touch screen apparatuses are widely used in various fields as input devices to replace keyboards or mice.
A general touch screen apparatus requires a direct touch on a display screen by a finger or a pen. However, as the size of a display apparatus increases, if a distance between a user and a display apparatus increases, it may be difficult to directly touch the touch screen. An optical touch screen apparatus may perform the same functions as a conventional touch screen apparatus by sensing light instead of touch by a finger or a pen. An optical touch screen apparatus may be useful not only for communication between a user and an apparatus but also for communication between users.
To embody an optical touch screen apparatus, fine-sized light-sensing devices for sensing light are used. An example of generally used light-sensing devices includes an amorphous silicon thin-film transistor (a-Si TFT). However, in a case of an a-Si TFT, the change in current due to light is insufficiently large. Therefore, charges generated by a photodiode during the application of light are accumulated in a capacitor for a predetermined period of time and a signal related to light intensity is generated based on the amount of charges accumulated in the capacitor. In this case, a sensing time may be delayed by as much as a period of time for accumulating charges in the capacitor, and parasitic capacitance may increase as the size of an optical touch screen apparatus increases.